docs(marker_shapes): fix shape default (None, not circle), scope note, substitute-your-names guidance

Author: timtreis

tutorials/marker_shapes.ipynb

@@ -95,7 +95,8 @@
    "source": [
     "## 1. The default — circles\n",
     "\n",
-    "Circle elements are drawn as circles. `shape=\"circle\"` is the default."
+    "The default is `shape=None`, which renders each element as its stored geometry — circles here.\n",
+    "Passing `shape=\"circle\"` is equivalent for circle elements."
    ]
   },
   {
@@ -185,7 +186,11 @@
     "\n",
     "Visium spots sit on a hexagonal grid, and are often drawn as touching hexagons rather than dots.\n",
     "`shape=\"visium_hex\"` does exactly that. We switch to the real Visium mouse-brain section and colour by\n",
-    "its brain-region clusters."
+    "its brain-region clusters.\n",
+    "\n",
+    "We switch datasets because the synthetic `blobs_circles` are not a real hexagonal grid. The element\n",
+    "name (`\"spots\"`) and the columns (`\"cluster\"`, `\"total_counts\"`) below are specific to this dataset —\n",
+    "inspect `sdata.shapes` and the annotating table's columns to find the equivalents in your own data."
    ]
   },
   {
@@ -242,7 +247,9 @@
     "## 4. Combining `shape=` with colour and outline\n",
     "\n",
     "`shape=` composes with the usual styling — colour by a column, add an outline, set `fill_alpha` (see\n",
-    "the *Styling shapes and labels* tutorial)."
+    "the *Styling shapes and labels* tutorial).\n",
+    "\n",
+    "(See the *Legends and colorbars* example for `legend_loc` and `colorbar_params`.)"
    ]
   },
   {
@@ -285,7 +292,8 @@
     "\n",
     "- Circle elements (Visium spots, `blobs_circles`) carry a centre and radius; `shape=` chooses the\n",
     "  marker they are drawn with, leaving the geometry unchanged.\n",
-    "- `shape=` accepts `\"circle\"` (default), `\"hex\"`, `\"square\"`, and `\"visium_hex\"`.\n",
+    "- `shape=` accepts `None` (the default, render as-is), `\"circle\"`, `\"hex\"`, `\"square\"`, and\n",
+    "  `\"visium_hex\"`; this tutorial uses circle elements (centre + radius), which `shape=` is designed for.\n",
     "- `shape=\"visium_hex\"` renders Visium spots as a touching hex grid — the familiar Visium look.\n",
     "- `shape=` composes with colour, outline, and the other styling arguments."
    ]